The incidence of the blood-brain barrier (BBB) damage, evident by blue staining of the brain tissue, was related to the duration of ischemia and to the duration of release following carotid occlusion. Thus e.g., in gerbils subjected to 6 hours ischemia, all animals showed the BBB damage 1 hour after release of occlusion. On the other hand, gerbils with 1 hour left carotid occlusion showed 100% incidence of the BBB damage only 20 hours following release of carotid clipping. Raising the systemic arterial blood pressure accelerated significantly the BBB damage; e.g., a 100% incidence of the BBB damage was evident in gerbils with 147.8 mean arterial blood pressure (MABP) within 15 minutes after release, whereas in animals with the normal MABP, such incidence was present only after 5 hours of release of carotid occlusion. The histological changes characteristic of ischemic damage clearly preceded the BBB injury.